WP Rocket Remove Unused CSS option

Hello,

I am using WP rocket and there is an option called Remove Unused CSS option. When I activate this option my web site become really fast but icons (e.g. email icon, phone icon, basket icon, search icon, setting icons and so on) getting disapper(displaying blank square). Also add to chart button doesnt work as it supposed to be. What is the reason of it ? I really want to use this option because it makes really fast my website.